In photovoltaic (PV) energy systems, inverters are used to convert DC electrical energy that is generated by photovoltaic panels to AC electrical energy that is compatible with the AC distribution systems that are built into the infrastructure of residential, commercial, industrial premises, and large ground mounted solar farms.
Typically an inverter is hard grounded (e.g., on the negative rail of the inverter DC input) and an isolation transformer is utilized in connection with the inverter to galvanically isolate the inverter from the AC power system of the premises and to provide a voltage ratio change. Transformers, however, add additional inefficiencies, complexity, weight and substantial cost to inverters.
For inverter applications large enough to warrant a dedicated connection to the utility (e.g., a utility transformer connecting the inverter to the utility's own medium voltage supply), it is often possible to remove the integrally provided transformer from the product. Although purchased as “transformerless,” the operation of such inverters is still predicated on the presence of an isolating transformer to allow for the traditionally hard-grounded PV array configuration. Although inverters have been marketed as being “transformerless” because, when sold, a transformer is not integrated with these inverters, the power distribution system (e.g., 480/277 VAC) of the premises is still isolated from the inverter by a utility transformer. As a consequence, these “transformerless” inverters still rely on a transformer for isolation and are typically limited to installations where medium voltage (e.g., 4160 to 13 KV) transformers are present at the premises.
There is not presently a large PV inverter (e.g., an inverter larger than 10 kW) intended to operate independent of any isolating transformer. Presently available equipment also does not allow inversion directly into 480VAC three-phase, but rather into much lower voltages that are ratio-changed to more useful voltages such as 480 Volts by the integrally provided transformer. Accordingly, a system and method are needed to address the shortfalls of present technology and to provide other new and innovative features.